1. Field of the Invention
The present invention relates to an image forming apparatus and a computer readable recording medium.
2. Description of Related Art
Some image forming apparatuses have configurations in which line sensors are disposed on conveyance paths of sheets and sheet surfaces are read by the line sensors to enable test and color adjustment of images formed on the sheets.
Color values such as RGB values obtained by image reading devices such as the line sensors are device-dependent values. Thus, the color values are generally converted into color values of standard color space such as L*a*b* values, which are not device-dependent, by using look up tables (LUTs) which are referred to as scanner profiles.
The scanner profiles can be created by reading, with image reading devices and colorimeters, color charts which were formed on sheets by image forming apparatuses, and associating the color values obtained by the image reading devices as input values with the color values of the standard color space obtained by the color measurement devices as output values.
Colors of images formed on sheets change according to temperatures of the sheet surfaces due to the characteristics of the color materials such as pigments used for the images. Conventional methods measure the change amounts of color values for respective devices in advance and correct, according to the change amounts, the color values which were obtained from the devices into respective color values under intended temperatures (for example, see Japanese Patent No. 5268542).
It is assumed that the temperatures of sheet surfaces also change at the time of creating the scanner profiles due to a series of image formation. Thus, in order to obtain a scanner profile with high accuracy of color conversion, it is necessary to correct color values for each device which change according to temperature.
However, the above correction of color values is effective only for colors for which the change amounts of color values according to temperature were actually measured. In reality, though a color chart having nearly 2000 colors such as FORGA and Japan Color is read for color adjustment in some cases, correction error is large for colors other than the colors having the change amounts measured in advance. Thus, effective correction according to temperature cannot be performed.
The change amounts can be newly measured for the colors which have change values of color values being not measured. However, it is troublesome to measure the change amounts of color values each time a color chart is formed. Furthermore, in order to avoid the increase in size of the apparatus, many image forming apparatuses have color measurement devices therein each of which reads only a part of the sheet surface, not the entire sheet surface. In this case, since the location of patches is limited within a reading range of the color measurement devices, the patches of a color chart need to be arranged on a plurality of sheets to be dispersed, waste sheets are increased, and thus, the cost is increased.